Article and process for wave damping



June 15, 1955 B. H. FOSTER ETAL ARTICLE AND PROCESS FOR WAVE DAMPINGFiled March 25 1961 2 Sheets-Sheet l om om INVENTORS BOUTWELL H. FOSTERHENRY F. MILLER ATTORNEY.

June 15, 1965 B. H. FOSTER ETAL ARTICLE AND PROCESS FOR WAVE DAMPINGFiled Maron 25, 1961 2 Sheets-Sheet 2 INVENTORS BOUTWELL H .FOSTERHENRYEMILLER mmf/5% ATTORNEY.

United States Patent Oiice 3,188,813 Patented June 15, 1965 ARTICLE ANDPRUCESS FOR NAVE DAMPNG This invention relates to a device for theattenuation of waves in liquids, such as waves which occur in the sea,in lakes, or in other large bodies of water, and to a method ofattenuating such waves. More particularly, this invention relates to theattenuation of liquid waves by the use of a wave-damping blanketcomprising multi-ply sheets of tough, permeable, resilient fabric. Thewavedamping blanket comprises a substantially dat multi-ply base sheetand a multi-ply upper sheet of corrugated configuration having peaks andvalleys therein, this upper sheet being secured along the valleysthereof to the flat base sheet. v

Heretofore numerous attempts have been made to reduce the height andenergy of sea waves. Successful damping of waves would offerconsiderable promise in numerous applications, eg., reducing thedestructive effect of waves in temporary harbors wherein refuelingoperations must be undertaken, reducing the height of waves in assaultoperations where beaches need to be protected, or in the open sea whererescue operations must be undertaken, and the like. Similarly,successful wave-damping would facilitate the creation of artificialharbors and shore construction in areas exposed to the open sea, wouldprotect offshore man-made structures such as offshore oil vrigs fromwave damage, etc.

Accordingly, it is an object of this invention to provide a device forthe damping of liquid waves.

Another object is to provide a novel method for the damping of liquidwaves.

Additional objects and advantages of this invention will become apparenthereinafter.

The foregoing objects are achieved by the use of a wave-damping blanketof special construction. The wavedamping blanket comprises asubstantially flat multi-ply base Sheet and a corrugated multi-ply topsheet having peaks and valleys, this sheet secured to the base sheetalong the valleys thereof. Both of these sheets are desirably made of acomparatively resilient, tough, permeable, buoyant, multi-ply fabricmaterial.

The method of attenuating waves in accordance with this inventioncomprises placing the Wave-damping blanket in the liquid in which thewaves are being propagated Lwith the top-most base sheet disposedbeneath the upper corrugated sheet. The inherent buoyancy of thewavedamping blanket is such that the peaks of the top-most corrugatedsheet will be at or just beneath the surface of the liquid. As the crestof the incoming wave advances the wave passes through the permeablefrontface of the corrugated sheet and the wave impulse is transmitted tothe body of liquid Within the foremost compartment of the blanket, thiscompartment being defined by the front face, back face, and peak of theforemost corrugation and by the base sheet between the valleys of thatcorrugation. The wave energy is transmitted to the body of liquidcontained in this compartment to thereby induce orbital motion of theliquid. Although the walls deiining this compartment are permeable andtherefore do permit passage of liquid therethrough, these walls also fexert a retarding or damping force upon the liquid, tending to break upthe orbital motion thereof. In this manner, each successive compartmentof the wave-damping blanket further damps the wave as it is transmittedtherethrough. That is, each compartment, by virtue of its tough,permeable construction, forms a partial containment for the orbitingmass of water within it, thereby interfering with the orbital motion andgradually damping the wave.

The particular geometry of the blanket is of considerable importance.Specifically, the corrugated permeable blanket of the instant inventionpermits ready access of the incident Waves into the damping compartmentsand yet exerts great containment forces upon the mass of water Withinthe compartment thrown into orbital motion by the wave impulse, so thatthe wave energy is dissipated. Passage of the waves through successiveblanket compartments further dissipates the wave energy, so that whenthe incident waves are finally transmitted at the downstream side of theblanket the wave energy, as evidenced by the wave height of thetransmitted wave, is greatly reduced.

JFor a better understanding of the nature of this invention referenceshould be had to the following detailed description when read inconjunction with the accompanying drawings, wherein:

FIG. 1 is a side view in perspective of one embodiment of thewave-damping blanket of this invention wherein the corrugations thereofare of substantially sinusoidal configuration;

FIG. 2 is a perspective view of a four ply fabric used for the upper andbase sheets of the device shown in FIG. 1;

FIGS. 3 and 4 are perspective views of a three ply fabric and a two plyfabric, respectively, used as the sheet material in alternativeembodiments of this invention;

FIG. 5 is a perspective view of an alternative embodiment of thisinvention wherein the corrugations are of saw-toothed configuration;

FIG. 6 is a side view of another embodiment of this invention whereinthe corrugations of the wave-damping blanket have a saw-toothedconfiguration; and

FIG. 7 is a schematic diagram showing the wave-damping blanket of FIG. 1in actual operation in a liquid.

The embodiment illustrated in FIGS. 1 and 7 includes a wave-dampingblanket generally designated by the iigure 1t) which is buoyant in theliquid in which the waves are being propagated. The blanket comprises asubstantially flat base layer 1?. and a corrugated sinuous upper layer14, containing peaks 16 and valleys 18 therein. The corrugated layer 14is stiched and lashed to the base layer 12 along the valleys 18 by meansof plastic cording 20. The leading edge of the bianket may be stiifenedby lashing thereto a metal tube 24. This tube also serves to spread theload of the mooring cable 26 across the entire width of the blanket.

The fabric used in both the upper and base layers of the wave-dampingblanket shown in FIG. 1 is shown in perspective in FiG. 2. This fabricis a four-ply fabric, the construction of which is fully described inU.S. application Serial No. 730,399, tiled April 23, 1958, by G. D.Martin, now Patent 3,009,232, the contents of which are incorporatedherein by reference. Briey, this fabric, generally designated by thenumeral 30, includes a first ply 32 including heat shrinkable syntheticyarns 34 and transverse yarns 36 interlaced therewith. A second -ply 38has heat shrinkable synthetic yarns 40 extending unidirec- .tionallywith yarns and transverse yarns 42 interlaced with yarns liti.

Many heat shrinkable synthetic yarns have a relatively high shrinkage,and consequently being suitable for the yarns 34 and 40 are well knownin the textile art. Examples of such yarns are: Branched polyethylene,as distinguished from the so-called linear polyethylene (an orientedpolymerized ethylene); Rhovyl (polyvinylchloride); saran--the so-calledhigh shrinkage type-(a copolymer of vinyl chloride and vinylidenechloride); Verel II (acrylonitrile copolymer), etc. 4In general theforealessia going bers will shrink or more at temperatures Vat or belowthe boil (212 F.) and are eminently suitable for the relatively highshrink yarns. Other high shrink vyarns are well known which willAshrinkan equivalent .amount atv higher temperatures, e.g., yarns `formedot x blends of branched and linear polyethylene.

in which Yit is suspended, comparative toughness and resiliency, etc.For example, several plies of plastic screening, i.e., plastic rneshedfabric,.may be secured to one Vanother to form a strong, buoyant,permeable multi-ply Disposed between plies 32 and 38, are plies 44 and-46, i.

each of which includes yarns which are less shrinkable than the yarns 34and 40 under thedesired vshrinking treatment, and .which are designated43 and 50, respectively, and which extend unidirectionally with yarns 34and 4i).k Yarns 48 are Vinterlaced rst, with selected ones of transverseyarns 36, as along lines 52, yand alternately with selected ones of.transverse yarns 42, as along lines- 54. Similarly yarns 50 areinterlaced first with selected ones of transverse yarns 36, asalonglines 55, which-is spaced from line 52, and alternately toselecteclones of yarns 42, as along lines 58. It willbe noted lines 56lie between two lines 52 where yarns 48 are joined to the first ply. Themanner of joining plies-44 and 46'to yply v38 is the same. lLines '52,S6 and 54, 58 ofV interlacin'gs,v yeach will comprise one or moretransverse yarns 3S, 42;

for example, two transverse yarns 38 ymay interlace with lyarns 4S ateach line .52.' Y H 1 Many yarns which shrink less than the heatshrinkable synthetic yarns 134, 40 at a suitable shrinking treatment arewell'known to the textile art. For example ifthe Yheat shrinkingtreatment Vis to be a shrinkage in'boiling water, and one of the yarnshereinabove mentioned which shrinks the requisite amount undery Vthistreatment is selected' for the heat shrinkable synthetic yarns, thefollowing bers may be used for the less shrinkable yarns V4S, 5t):nylon, (polyamide); Saran-the so-called regular `type;rDacron (anoriented polyester of terephthalic acidV with ethylene glycol); etc. n,

Between plies 32, 38, additional transverse yarnsvtl, 62 interlace onlywith the less shrinkable yarns 48,' 5t) respecfabric sheet. Two of suchsheets can be then used in the construction of the wave-damping blanket,one such sheet as the upper corrugated sheet and the other as the iatbase sheet. Y

Another embodiment of ,this invention utilizes a wavedarnping blanketwherein the upper ply exhibits a sawtoothed corrugation rather than asinusoidal corrugation.

Y This embodiment is shown in FIG. v5. The saw-toothed .to incident wavelength.

rblanket'ltlt) functions in essentially thev same manner as the sinuousblanket illustrated in FIGS. l and 7, the triangular compartmentsserving Yas partial containments for the orbiting liquid therewithin. Ai

lt is desirable that the overall length of the wave-dampging blanketexceed the wave length of the incident waves,

i.e., the distance between successive Wave crests. If a single blanketassembly-unit has a length less thany the .wave length of the incidentwave,fseveral such assemblies may be lashed together yto provide .thenecessary length.

i The joints betweenV successive blanket assemblies may be l ',sirablylashed'to one another at close intervals, both at tively. Many yarns aresuitable for the transverseyarns 60, 62 and 36 and 40; for example, theless shrinkable Hibers noted above are highly satisfactory. -1

It Ywill be seen that plies 44, 46 intersect each other Vperiodicallyalong lines Which'have been designated 64 inthe drawing. In oneembodiment, at the lines64, yarns 48 alternate with yarns 5t) across theWidth of the fabric,

and yarns 48, 50 lie closely-adjacent each other,i.e.,V inAabutting'relation'or-spaced less than the diameter of `a .yarn 48.0r5t) from each other alongline 64.Y f f The wave-damping blanketillustrated in FIGS. 1 and 7, wherein both the upper'and base layers aremade of the four-ply material, constitutes a preferred embodiment ofthis invention, for Vsuch four-ply material offers unusual toughness andresilience, yet is extremely permeable. Other types of multi-plyconstructions' are also suitable.

Two of suchconstructions areV shown'in FIGS. 3 and 4.. Referring to FIG.3, a .three-ply fabric '70 comprises'aV top ply 72', a bottom ply 74,and an intermediatel ply 76.

the transverse yarns 80 ofthe top and-bottom plies are made ofrelatively lesss'hrinkable material.

the outside edges and at spaced intervals at the interior. l,By thusplying up individual Vblanket assemblies any desired overall thicknessmay be readily secured. In general, the greater the thickness of theWave-damping blanket, the shorter the overall length required. Ofcourse, the Vparticular degree of waveheight attenuation desired Y,to-besecured Willalect theiblanket'design. Consequent- 5 1s-morey thansuclent, for this represents an Venergyzat- Desirably both the top andbottom plies; each include V` Aheat shrinkable synthetic yarns 7 8extending unidirection-l ally of one another, whereas Vthe intermediateply.76 and ly, where only a slight degree of wave height attenuation,is-required,the Vabove'r'equirernents as to blanket thick- Vness and.vlength may be substantially reduced. In most instances,a wave heightattenuation of aboutv 80 percent tenuation of Vabout 96 percent, i.e.,the wave energy is fproportionalV to the square ofthe wave height.

Y In accordance with another embodiment of this inv 50; Vention, awave-damping blanket 110 of variable thickness is provided. This.stepped construction is illustrated in FIG. 6. Maximum blanketthickness is provided at the frontportion of the blanket.(nearest theincident Awave) Aby plying up several individualV blanket assemblies.

'- the incident wave.

This increased Vthickness permits heavy initial damping of As the waveprogresses through the lincreased thickness of the first part of theblanket more ,wave energy is dissipated-than would ybe the case in avsingle laye/1 blanket and less blanket thickness is required FIG. 4shows atwo-plyV fabric 90, comprising VaV bottom j wise of the ply,whereas V'the top ply 94 and the transverse yarns 98 of the bottom ply92 The nature of both the three-ply and two-plyy construc- ,tions ismore fully described in U.S. Patent No. Re. Y .24,007 yto B. H. Foster,issued May 24, 1955, the contents Vof which are incorporated herein byreference. l

are made of relatively-less Yshrinkable material. l

.Iply 92 and atop ply 9.4. Desirably the bottom ply Vincludes heatshrinkable-synthetic yarns 96 extending length- Of course, othermulti-ply fabric constructions may be .used in the construction of thewave-damping blanket," j provided the resulting fabric exhibits therequisite physical characteristics, i.e. permeability, buoyancy intheliquid inY succeeding sections of the blanket. Accordingly, the

4.thicknesses are graduallyfstepped down over the length of the blanketby reducingl the number of plied up'blanket assemblies, as shown in FIG.6. Although it is not believeclr a substantial reductionV can beeffected in quantity `Yof blanket required to dampva given Wave by usingthe embodiment of FIG.V 6, that` embodiment, or another multi-layerarrangement, Apermits a reduction in overall f length of the deviceWherev'that may hel necessary or desirable.

The operation of Ithe wave-damping blanket will be de- 'scribed withreference, by way of illustration, tothe sinuous wave-damping blanketshown in FIGS. y1 and 7. In vorder to damp VWater waves the wave-dampingblanket 10 'is placed in the body of water in which the waves are beingpropagated; the natural buoyancy ofthe blanket being such that the peaks12 of the top-most sinuous upper layer 14 lie at about the surface ofthe water. The blanket is moored in position by mooring cable 26, withthe `trailing edge of the blanket (the righthand edge as seen in FIG. 7)immediately adjacent the `area where the calm water iS desired. Theincident wave approaches the opposite (front) end of the blanket, i.e.,containing the tube 24. The crest o-f this wave passes through thepermeable front facey 15 of the corrugated sheet 14. The wave energy isthus transmitted to the body of water contained within the foremostcompartment of the Wave blanket, i.e., that compartment defined by thefront face 15, rear face y17, yand peak l16 of the corrugated sheet andby that portion 13 of lthe base sheet 12 between the valleys 18' and 18,thereby inducing orbital motion of the liquid With-in this compartment.The permeable walls .15, 16, 17 and 13 defining this compartment permitpassage of water therethrough. However, the flow resistancecharacteristic of these walls tend .to disrupt the wave-induced orbitalmotion Aof the water thereby dissipating the wave energy and damping thewave. Successive compartments in the blanket function in like manner tofurther damp the wave as it gradually traverses the length of theblanket. Of course, where several blanket assemblies are plied up withone another to provide increased overall blanket thickness, the lowerblanket compartments also contribute to .the damping of the waves.

It will be noted that in the schematic illustration sho-wn in FIG. 7 theblanket length exceeds the wave length A, i.e., the distance betweensuccessive wave crests.

. 0f course, multi-ply fabrics such as the three-ply and two-ply fabricsshown in FIGS. 3 and 4, respectively, may be used instead of thefour-ply fabric shown in FIG. 2 to make up the upper and base sheets ofthe blanket. Alternatively, .several plies of plasticv screening may beused, so long as the essential requirements of the `iinal upper and basesheets of the blanket `are satisiied, i.e., liquid permeability,resilience, strength, land buoyancy.

Similarly, the saw-toothed corrugation shown in FIG. 6 may be utilizedin place of the sinuous corrugation previ- -ously described.

lIn `order t-o construct the wave-damping blanket of the instantinvention it is necessary to cause the upper :sheet to conform to acorrugated conguration. One convenient method for securing such aconguration is to incorporate one or more draw strings longitudinally ofthe upper sheet, this sheet also being provided with a plurality ofstops for the draw I.strings at spaced positions over the length of thesheet. As the draw string is pulled the sheet is caused to bunch up toform a sinuous corrugated contfigurat-ion. The height and length of thecorrugations is controlled by the placement of the stops and the degreeof tightness to which the draw string is drawn. Once the corrugationsare formed, the valleys thereof are securely lashed and stitched to thebase sheet.

The dimensions of the compartments formed by the corrugations of theupper :sheet and the base .sheet may vary, depending upon the relativetoughness, strength, resilience, and shape-retention characteristics ofthe particular permeable multi-ply fabric material used to make thesesheets. Naturally, the height of the corrugations and the distancebetween adjacent valleys thereof .should not be of such proportions thatthe compartments formed thereby substantially lose their shape-retainingcapacity when placed in the liquid in which the Waves are beingpropagated. It has been found that particularly good wavedamping isobtained when the corrugation height, i.e., distance from thecorrugation peak to the bottom of the base sheet, is from about 4 to 10inches and correspondingly the distance between adjacent valleys is fromabout 6 to 12 inches. Of course, constructions falling outside theseranges may also be suitable in certain instances. However, blanketscontaining compartments `of smaller size, while operative, tend to beuneconomical.

The following specific examples will fur-ther illustrate the invention.

In the preferred embodiment the layers 12 and 14 of the blanket 11) areeach made up of the four-ply fabric shown in FIG. 2. The heat-shrinkablesynthetic yarns 24, 40 are made up of branched polyethylene. The lessshrink- `able longitudinal synthetic yarns 48, 50 are made up ofpolypropylene. The less `shrinkable transverse yarns 36, 42 are made upof a blend Iof branched and linear polyethylene. The yarns have adiameter of from about 0.014 to 0.020 inch. The thickness of thefini-shed four-ply layer of fabric (FIG. 2) is about one half inch. Thefabric is inherently slightly buoyant in `fresh water. Two such fabriclayers are used to form the blanket assembly of FIG. 1, one layer forthe base `sheet i12 and another from the sinuously corrugated layer 14.The corrugated sheet is stitched and lashed along the valleys to thebase sheet with plastic cording. The blanket assembly is about eightinches thick (from the peak to the bottom of the base sheet) and thedistance between adjacent valleys is about 12 inches. The tubing i-ssecurely lashed to the blanket assembly as shown in FIG. 1. The basicblanket unit is about eight feet four inches long and nine feet wide.These basic units are lashed together -to form blanket assemblies havinglengths of 16.6, 25, 33.4, and 50 feet. The leading edge of the blanketassembly is additionally .stitfened by lashing a metal tube 24 theretoas shown in FIG. 1 to thereby spread the load of the mooring cable 26across the blanket width.

iIn certain instances involved multiple layers Iof the basic blanketunit are used, with the individual layers being securely lashed at closeintervals around `the outside edges of the stack of blanket units and atspaced intervals in the interior. Mooring stiifeners are provided acrossthe front of the top and bottom layers of these `stacked units. Testsare reported for a two-layer blanket of 16 inch total thickness, athree-layer blanket of 24 inch total thickness, and for a steppedblanket which was three layers or 24 inches thick at the front end, twolayers or 16 inch thick at the midsection, and one layer or 8 inch thickat the trailing end. In this three-step blanket each thickness has alength of 16.6 feet thus providing a total length of 50 feet.

Test results are tabulated in Table I. The uniformly high degree of waveattenuation is apparent.

TABLE I Inci- Trans Wave N o. of Blanket Blanket Wave dent mitted HeightExample Blanket Depth Length Length Wave Wave Atten- N o. Layers (feet)(feet) (feet) Height Height nation (feet) (feet) (percent) 1 0. 67 25 50. 2l. 0. 001 99 l 0. 67 33. 4 l() 0.62 0. U6 90 l 0. G7 50 20 l. 19 O.25 79 2 1. 33 33. 4 l0 1, 01 0. 04 96 2 l. 33 25 l0 0. Sl 0. 07 92 3 2.(IO 25 20 0. 89 O. 1S 80 3 2. 00 50 30 0.91 0. 14 84 3 2. 00 50 40 0. 680. 15 77 Step l. 33 50 10 0. 96 0. 03 97 Step 1. 33 50 20 1.21 0. 16 87Step 1. 33 50 30 0. S6 0. 19 77 Step 1.33 50 40 0. 69 0. 19 75 Havingthus described the invention, what is desired to be protected and herebyclaimed is:

1. A device for damping liquid waves, comprising a frexible,liquid-permeabie flat base sheet, an upper, ilexible, liquid-permeablesheet of corrugated configuration having peaks and valleys, said uppersheet contacting and being secured along the valleys thereof to saidflat base sheet, the distance from the said peaks to the bottom of saidbase sheet being from about 4 to about l() inches and the distancebetween adjacent said valleys being from about 6 to about 12 inches,both of said sheets being made of a buoyant, multi-ply, flexible,liquid-permeable fabric including a corrugated fabric ply, and both ofsaid sheets being equal in length at least to the wave length of thewave to be attenuated, stiifening means for an edge of the fabricsecured to'the device .alon'gone vedge thereof, and means attachedthereto toY moor the n vdevice in a body of liquid. v n

2. The device of claim 1 wherein each multi-ply fabric sheet comprises`a substantially planar irst and second ply,

- 8 4upperandbase multi-ply fabrics each comprise a substantially'planar' first ply and an undulated second ply disposed along Vone sideof and periodically interlaced with .said first ply. y I Y 10. The'wavedamping device of claim 1 wherein said upper and base multi-ply fabricsYeach comprise a first ply, which ply includes heat shrunksynthetic'yarns and transye'rse yarns interlaced therewith, a secondundulated ply disposed along one side of said irst ply with theundulated yarns in said ply extending unidirectionally with said heatshrunk synthetic yarns, each'of said undulated plies being interlacedperiodically Vwith said'iirst plypto tie said two between said lirst andsecond plies and spacing said first ,Y

and second plies from one another, the peaks and .valleys of saidthirdundulated ply being disposed opposite the i valleys and peaks,respectively, of said fourth undulated ply.

4. The device yof claim 1 sheet comprises. a rst and second ply, eachply including heat shrunk synthetic yarns and transverse yarns inwhereineach multi-ply fabricV terlaced'therewitm the heat shrunk syntheticyarns inthe first plyV extending unidirectionally with the heat shrunksynthetic yarns in the second ply, a third andV fourth ply,

each of said third and fourth pliesy being undulatedand disposed betweensaid first and second plies with the un- Y ydulated'yarns in said pliesextending unidirectionally Vwith )said heat shrunk synthetic yarns, eachof said undulated .plies being interlacedY periodically and' alternatelywith said rst and second plies to tie said four plies into a unitaryfabric, said heat shrunk synthetic yarns maintaining said undulatedyarns inan undulating state, the undulations in said yarns spacing saidfirst and second plies from Aone another. 5. The wave damping device ofclaim 4 wherein said heat shrunk yarns comprise branched polyethyleneand said undulated yarns comprise a linear polyoleiin.

6. The wave damping device of claim 1 wherein a plui rality of uppersheets and base sheets are secured to one another. Y

7. The wave damping device of claim 1 wherein'said upper and basemulti-ply'fabrics each comprise a substantially planariirst and secondply and an undulated thirdy ply disposed therebetween, theundulations insaid third Vply spacing said first-and second plies from one another.

8. The wave damping device of 'claim 1 wherein said upper and basemulti-ply fabricseach comprise affrst and second ply, each ply includingheat shrunk synthetic yarns and transverse yarns interlaced. therewith,the heat shrunk syntheticzyarns inthe lirst ply extendingunidirectionally vwith Vthe heat shrunk synthetic yarns. in the secondply, `a third undulated ply disposed between said first and second plieswith the undulated yarns in saidV plies into'a unitaryw fabric, saidheat shrunksynthetic yarns maintaining Vsaid undulated yarns in anundulated state so that therpeaks of said undulated yarns are disposedin parallel spaced relation from said first ply.

j` 11. Thewave damping device of claim y1 wherein each of said multi-plysheets comprises afplurality of plastic jmesh screensY secured 'to' oneanother.

12., The wave damping device of claim 1 wherein said 'corrugatedsheet'is substantially sinusoidal in nature. 513.]Thewave damping deviceof claim 1 wherein said 'corrugated sheet is substantially saw-toothedin nature.

14. A method 'of damping liquid waves which corn- Vp'rises'iioatinginthe liquid inWhich'the waves are formed 'thewave-damping' device asldefined by claim 1 with the basevsheet of said device disposed beneaththe upper sheet and the'thickness of the device lbeing at least 15% ofYthe overall depth of the liquid in which it is suspended, ymooringthedeyice` in'suchliquid, permitting the wave impulse to enter'the'spacecompartment between the base sheet ,and the foremost corrugation of theyupper sheet, theY wave impulse entering said space compartment by'passing through the permeablev front face of the corrugated sheet andtransmitting itswave energy to the liquid within the compartment tothereby impart orbital motion thereto, and damping ythe `Wavebypermitting the permeable space compartment Vto ypartially contain theliquid vtherewithinl and to interfere with the orbital motion of saidliquid, successive damping being. permitted to occur by the gradualpassage `of ythe vwave impulse through suc- Vcessive space compartmentsof the 4wave-damping device.

y 15. The method of'claim 14 wherein a device having a length atleastthree times the distance between succes- `sive wave crests ofwthe liquidWave is so floated.

f References Cited by -the Examiner i VUNI'ID STATES PATENTS 2,327,1848/45 ooodiow. 42,464,154 3/49, Roselius; 2,607,104 `8/52 Foster -v 28-722,644,777.v 7/53vk Havens 154-459 3,009,232 l11/61 Martin 28-723,029,606 4/62 olsen Y 61-5 i Y f FOREIGN PATENTS I' 590 1/86 GreatBritain.'

VEARL I. WITMER, Primary Examiner.

JACOB L. NACKENOFF, JACOB sHAPrRo,

Y Examiners.

1. A DEVICE FOR DAMPING LIQUID WAVES, COMPRISING A FLEXIBLE, LIQUID-PERMEABLE FLAT BASE SHEET, AN UPPER, FLEXIBLE, LIQUID-PERMEABLE SHEET OF CORRUGATED CONFIGURATION HAVING PEAKS AND VALLEYS, SAID UPPER SHEET CONTACTING AND BEING SECURED ALONG THE VALLEYS, THEREOF TO SAID FLAT BASE SHEET, THE DISTANCE FROM THE SAID PEAKS TO THE BOTTOM OF SAID BASE SHEET BEING FROM ABOUT 4 TO ABOUT 10 INCHES AND THE DISTANCE BETWEEN ADJACENT SAID VALLEYS BEING FROM ABOUT 6 TO ABOUT 12 INCHES, BOTH OF SAID SHEETS BEING MADE OF A BUOYANT, MULTI-PLY, FLEXIBLE, LIQUID-PERMEABLE FABRIC INCLUDING A CORRUGATED FABRIC PLY, AND BOTH OF SAID SHEETS BEING EQUAL IN LENGTH AT LEAST TO THE WAVE LENGTH OF THE WAVE TO BE ATTENDED, STIFFENING MEANS FOR AN EDGE OF THE FABRIC SECURED TO THE DEVICE ALONG ONE EDGE THEREOF, AND MEANS ATTACHED THERETO TO MOOR THE DEVICE IN A BODY OF LIQUID. 